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Re: [Assimp-discussions] Is it not possible to calculate tangents with generated normal?
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From: Nicolas L. <nic...@ou...> - 2013-07-22 23:45:11
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Okay, sounds good then. For my application, I just need any tangent vector. So that means, any vector perpendicular to the normal. Finding that is an easy matrix calculation so I'll just add it when I'm processing each vertex. Thanks for the info though. ________________________________ From: Thomas Schulze<mailto:th...@dr...> Sent: 7/22/2013 18:19 To: ass...@li...<mailto:ass...@li...> Subject: Re: [Assimp-discussions] Is it not possible to calculate tangents with generated normal? Nope, sorry. Tangents and Bitangents are *defined* to point along the texture axises. They're used to convert between model space and tangent space for normal mapping and about any other per-pixel shader effect. You can't have those without texture coordinates. Bye, Thomas Am 23.07.2013, 00:12 Uhr, schrieb Nicolas Leroux <nic...@ou...>: > It looks like you’re right: > > > “Vertex tangents. > The tangent of a vertex points in the direction of the positive X > texture axis. The array contains normalized vectors, NULL if not > present. The array is mNumVertices in size. A mesh consisting of points > and lines only may not have normal vectors. Meshes with mixed primitive > types (i.e. lines and triangles) may have normals, but the normals for > vertices that are only referenced by point or line primitives are > undefined and set to qNaN. See the mNormals member for a detailled > discussion of qNaNs. ” > > > I can only assume the same is true for bitangents. > > > Hmm, okay then, so shouldn’t the discussion we be having about > correctness: Wouldn’t it be pretty much trivial to calculate tangents > without the texture coordinates? I remember doing it in a graphics class > back in college, but I feel fairly confident that I could code it up if > needed. > > > Just thinking out loud now, this seems like a good discussion to have. > > > -Nico > > > > From: Martti > Sent: Monday, July 22, 2013 4:39 PM > To: ass...@li... > > > The tangent vector is the vector that represents the UV x-axis in model > space and binormal is the UV y-axis in model space, so I think there's > no way to compute them without having some form of texture coordinates > available. I may be wrong though. > > > > > On Tue, Jul 23, 2013 at 12:16 AM, Nicolas Leroux > <nic...@ou...> wrote: > > > > > You got it, the problem is that the mesh has no UV coordinates. > > > My question is: Why is this a problem? Aren’t vertices and faces enough > to generate tangents and bitangents? > > > The more I think about this, the more it looks like I’ll have to write > some tangent generating code that runs when I’m copying the vertices > over to my DirectX format. Do you know of a better solution? Don’t worry > about it if it’s late :P, I can definitely wait some time for your free > help. > > > I really appreciate the help, thank you. > > -Nico > > > > From: Martti > Sent: Monday, July 22, 2013 4:14 PM > To: ass...@li... > > > > > > > It is late here, so I may be of little help right now, but the tangent > generating postprocessing step seems to fail on three conditions: > > 1) mesh has no normals (clearly not it) > > 2) mesh primitive type is not triangle/polygon > > 3) mesh has no uv coordinates > > > > > In any case the CalcTangentsProcess seems to notify the logger of any > problem, so check if anything gets logged. > > Hope this helps. > > > > > > > On Mon, Jul 22, 2013 at 11:50 PM, Nicolas Leroux > <nic...@ou...> wrote: > > > > > I apologize, I’m going to have to update this again. > > > It appears that despite having normals and then applying the > CalcTangentSpace post process step, the tangents are still not getting > generated. > > > This screenshot sums up the situation pretty well: > http://i.imgur.com/DD3thr5.jpg > > > Thanks again for reading and sorry for the spam, I should’ve waited and > tested before screaming ”Success!” > > > -Nico > > > > From: Nicolas Leroux > Sent: Monday, July 22, 2013 3:18 PM > To: ass...@li... > > > > > > Ouch, I read the manual a bit closer and answered my own question quite > quickly. > > It looks like running this function AFTER generating the normals will do > the trick: ASSIMP_API const aiScene* aiApplyPostProcessing ( const > aiScene * pScene, > unsigned int pFlags) > > > http://assimp.sourceforge.net/lib_html/cimport_8h.html#a09fe8ba0c8e91bf04b4c29556be53b6d > > > Sorry for the 2 emails. > > > > From: Nicolas Leroux > Sent: Monday, July 22, 2013 3:01 PM > To: ass...@li... > > > Hello all, > > > I’m pulling in models that, more often than not, have no normal and no > tangents. I was disappointed to see this line in the comments for > aiProcess_CalcTangentSpace: > > > "Does nothing if a mesh does not have normals.” > > > The problem here is, my mesh does have normals, but they were just > calculated by > > aiProcess_GenSmoothNormals . > > > Is there any way to do an additional post process pass after generating > the normals? I could definitely write code to generate tangents myself, > but I trust the assimp teams tangent generating skills more than mine 😊. > > > Thanks in advance guys, > > Nico > > ------------------------------------------------------------------------------ > See everything from the browser to the database with AppDynamics > Get end-to-end visibility with application monitoring from AppDynamics > Isolate bottlenecks and diagnose root cause in seconds. > Start your free trial of AppDynamics Pro today! > http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk > _______________________________________________ > Assimp-discussions mailing list > Ass...@li... > https://lists.sourceforge.net/lists/listinfo/assimp-discussions ------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk _______________________________________________ Assimp-discussions mailing list Ass...@li... https://lists.sourceforge.net/lists/listinfo/assimp-discussions |
